As is known in the art, peening is the process of impacting a metal component with small particles generally at a right angle to the surface to be treated so as to thereby impact the surface of the metal in a direction normal thereto. The peening of the metal surface results in the material being stronger and tends to place the material in compression and relieve preexisting tensile stresses which may exist in the member. In other words, the impacting of the surface tends to place the same in compression and helps prevent fatigue, cracks and other imperfections in the surface from propagating through the surface to cause failure. The process in widely used in the aeronautical industry.
Conventional shot peening requires extensive blasting equipment and is not particularly suited to situations which require mobility of the equipment. Furthermore, in many such situations, the particles are not easily collected for recirculation. Rotary tools for shot peening are known in the art and are more adapted for applications requiring mobility. The tool will comprise a rotating shaft having drive means associated therewith and one or more flaps are attached to the shaft. Each flap has one or more hard particles or shot and the flap impacts on the work piece. Each impact produces a localized compressive stress on the surface for the reasons set forth above.
Conventional rotating peening tools are generally light weight hand tools which use a plurality of peening flaps mounted on the shaft. Each flap has one or more shot peening particles affixed to its free end and the flap is driven to impact the work surface as the flaps rotate. The art shows many different arrangements for the shot on the rotating flap.
As in any treatment, it is important to have proper control associated with the rotary peening treatment. In particular, the speed of rotation is critical in this process. At the present time, this is extremely difficult to provide since no speed controller exists.
In particular, one operator may hold the tool closer to the work piece and thus, the peening flaps strike the member to be treated at a slower pace—i.e. the rotational speed is decreased as the flap expends more energy to move past the work piece. Inversely, if the tool is held at a greater distance from the work piece whereby the outer portions of the flaps are utilized, the speed will be greater. Furthermore, the rotary peening apparatus frequently uses compressed air which often is provided through large compressors feeding several lines. When the demand on the compressor increases, the pressure in the lines might drop affecting the speed of the rotary peening apparatus.
Both the operator stability and the compressed air pressure variation, as well as several other factors, will have an impact on the speed of the rotary peening apparatus. This will have an influence on the energy transferred to the material and must therefore be kept as constant as possible to ensure a quality peening process.